The purpose of this study is to explore the relationship between self-esteem, narcissism, psychopathy and aggression to aid our understanding of personality factors that precipitate aggression. Further research into factors associated with aggression is urgently required due to the huge economic and personal costs of this behaviour. This is the first time these relationships have been explored in a unique and hard to treat population who are at high risk of harming others. Fifty inpatients of a high secure psychiatric hospital completed self-report measures of personality traits and completed a computerised task measuring implicit self-esteem. Information regarding previous and institutional aggression was obtained from patients’ medical files. Self-esteem fragility did not predict high levels of physically aggressive behaviour. However the findings suggest that narcissism and explicit self-esteem may play a role in institutional aggression. A profile of high explicit and high implicit self-esteem was found for Factor 1 psychopathy, and high explicit self-esteem was associated with adaptive narcissism. These findings suggest that narcissism and psychopathy have different self-esteem profiles. Alternative measures of implicit self-esteem in high secure populations are required to further test hypotheses relating to self-esteem fragility and aggression.